Extrusion system

ABSTRACT

A high pressure, high temperature extrusion apparatus generally includes a pressure means, such as a piston arrangement, for forcing an extrusion material such as a mixed metal powder, through a die which is maintained at a high temperature. A jacket surrounds and supports the die. A pressure responsive, feedback mechanism, control means surrounding the jacket which means are adapted to apply external force to the outer portions of the die, of a sufficient magnitude to counter-balance the inner extrusion forces.

United States Patent Aisenberg et al. [4 1 July 11, 1970 s41 EXTRUSION SYSTEM 3,364,717 1/1968 Green ..72/2s3 893,70l 7/l908 Benjamin min/27: [m 3,243,985 4/]966 Green .32/260 Pepperell, both of Mass. [73] Assignee: Whittaker Corporation, Los Angeles, p'ima'Tfimmimrmle-s Lanham Calif. Assistant Examiner-R. M. Rogers Au '--Do aid B. Nist 221 Filed: March 23,1970 211 Appl. No.: 21,702 I 1 ABSTRACT A high pressure, high temperature extrusion apparatus 52 U.S. Cl ..12/20 72/21 72/28 Senmuy includes a Pressure means such as Pisw" armlemerit, for forcing an extrusion material such as a mixed metal 51 1 Int. Cl .nzlb 37/08 B2 ic 31/00 Pwde a which is mainained a high sx Fleldulfiew'th M 72/21 l9 27 1 20 23 29 A jack surmunds and A responsive, feedback mechanism, control means surrounding the jacket which means are adapted to apply external force to I. gimme! UM the outer portions of the die, of a sufficient magnitude to UMTED STATES p -n; counter-balance the inner extrusion forces. 3,364,718 l/l968 Green ..72/253 9Clalns, l 35 30 EXTRUSION SYSTEM BACKGROUND OF THE INVENTION The present invention pertains to a means and method for extruding a material, such as a metal or plastic, through a die. In particular, the invention is concerned with a pressure responsive, feedback arrangement associated with the extrusion apparatus and adapted to prevent damage of the extrusion die due to excessive internal pressures.

A high pressure, high temperature extrusion process involves forcing an extrusion material through one or more extrusion dies. The extrusion material is usually maintained at a high temperature in order to facilitate the extrusion and forming process. The extrusion die itself is also maintained at a high temperature by either the extrusion material itself or by externally applied means. If the die were not maintained at a comparably high temperature, there would be a very marked temperature gradient of of the extruded material as well as a rapid cooling of the extruded material. Since the mechanical strength of the die decreases rapidly with temperature increases, the outer portion of the die has conventionally been massive and maintained at a relatively lower temperature. The inner portion of the extrusion die usually comprises a high temperature material imbedded in the relatively massive outer portion of the die.

The inner portion of the die which is in contact with the extruding material normally has a relatively high ductility and a relatively low strength. Consequently, such existing extrusion dies have a tendancy to deform and crack as a result of the extrusion forces applied. This tendancy is further aggravated by the large temperature gradient that exists in the die since the internal surface of the die is maintained at very high temperatures while the supporting portions of the die are maintained at lower temperatures. These resultant thermal stresses can be very severe under these particular conditions. With existing extrusion apparatus there is also a problem in maintaining the outer-most portions of the die at a sufficiently low temperature to prevent expansion of the inner portions of the die which are maintained at a higher temperature and have less ability to withstand cracking forces. Under repetitive operation, existing dies often have become damaged after only limited use.

Attempts to solve these problems by matching the coefficients of expansion of the heated portions and of the supporting portion of the die to thereby minimize cracking, are difficult and uncertain.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide an improved means and method for extruding a material into a die.

It is further an object of the present invention to provide an extrusion system that eliminates many of the problems associated with known extrusion apparatus as set forth above.

It is another object of the present invention to provide a extrusion die arrangement including a pressure responsive feedback mechanism adapted to prevent cracking of the die.

Still another object of the present invention is to provide an extrusion system that is rugged, inexpensive, easy to fabricate, install and maintain.

According to the invention, the extrusion system includes a pressure means for forcing an extrusion material which is maintained at a high temperature, under high pressure through a pre-formed die which may also be maintained at a high temperature. A jacket surrounds and supports the die and is maintained at a significantly lower temperature with reference to the temperature of the die itself. Pressure responsive feedback means surround the jacket and are adapted to apply an external force to the outer portions of the die, of a sufficient magnitude to counter-balance the inner extrusion forces generated by the pressure means.

The method of the present invention is characterized by the application of an external force to the outside of the jacket.

The externally applied force may be responsive to both the applied extrusion pressure force and any fluctuation detected by a displacement sensor located as part of the internal portion of the die.

BRIEF DESCRIPTION OF THE DRAWING Numerous other objects and advantages of this invention will now become apparent upon a reading of the specification in conjunction with the drawing in which the single FIGURE diagrammatically shows one arrangement for implementing the extrusion system of the present invention.

DETAILED DESCRIPTION The extrusion system illustrated in the drawing includes a pressure means for forcing the extruded material through a die. The extrusion system also includes first and second feedback means, 1 and 2 respectively. The first feedback means I senses the applied pressure and applies a counter-balancing pressure to the outside of the die. The second feedback arrangement 2 connects from a displacement sensor located in the inner portion of the die, to the outer portion of the die and is responsive to die displacements caused by internal extrusion forces.

Piston driver 14 is conventionally coupled to piston 16 and is adapted to force piston 16 against extrusion material 36 which is subsequently forced through die 34. The extrusion material enters input end 34A of die 34 and is constricted to a smaller size and extrusion shape of conventional nature as it leaves output end 348 of die 34. The high temperature die 34 also includes an outer portion or supporting jacket 30 having a pressure responsive surface 31. Thermal insulator 38 may also be provided between the internal portion 33 of die 34 and outer portion or supporting jacket 30, as shown. In addition, heating means may be externally provided, for causing the heating of the die itself. This external heating means may be a small furnace and is only needed when the extrusion material is not hot enough to cause the heating directly. Suitable and conventional thermostatic controls may be provided. Heater 40 may be used. In the single figure heater 40 is shown.

The supporting jacket 30 includes pressure responsive means 30A either of the pneumatic or hydraulic type. This means may comprise an annular fluid filled jacket as illustrated that is responsive to pressure from a pressure generator 24 or amplifier 20 to unifonnly apply forces to the inner portion of the die. The amount of pressure to be applied to the inner portion 33 of the die is controlled in the embodiment shown by the two feedback means 1 and 2.

Mechanical sensor 18, of conventional design, may be connected to the piston driving means or associated mechanism to cause variations in the forces applied to the piston. This output of the sensor 18 is amplified by amplifier 20 which may comprise a pneumatic or hydraulic amplifier and is fed to means 30A through pressure control valve 21. Since most materials are better able to withstand compressive forces than tensile forces the die need not be as massive as would be the case where only tensile forces were being applied. Since the internal force is determined by the pressure generated by driver 14 and the area of piston 16 it is possible to maintain the external compressive forces at a greater value than the applied force by the proper selection of piston area. In some cases it may be necessary and desirable to use adjustable pressure control valves as part of both force feedback paths.

The second feedback system 2 includes hydraulic or pneumatic pressure generator 24, amplifier 26 and feedback control valve 28, all of which are enclosed in a loop between die displacement sensor 32 and means 30A. During the extrusion process as the extrusion material is forced through die 34 internal portion 33 tends to displace outward. When this occurs die displacement sensor 32 detects any displacement change and sends a signal to electronic amplifier 26, The output of amplifier 26 is fed to pressure generator 24 which detects the signal and applies a counter-balancing force to the means 30A. The output of generator 24 may be varied by valve 28. In this way the supporting jacket force can be very carefully tailored to the values necessary to prevent or nimimize displacement for high temperature extrusion die, with consequent reduction in die fracture. Further, this may be accomplished electronically.

Rather than providing a rigid supporting structure for the die which is expensive and difficult to fabricate and install, the supporting structure disclosed herein is controlled by electronic means consisting of a displacement sensor, and an electronic amplifier. The system is also provided with fluid pressure control means and a hydraulic system, or the like, to which corrective forces are applied to the die to oppose any tendency of the die to expand outwardly. The feedback means prevent the imposition of excessive compressive forces and permit the simulation of an extremely rigid supporting structure. With the system disclosed herein, the efi'ective high temperature moduli of elasticity and the temperature coefficients of expansion of the die are made orders of magnitude closer to the ideal value required for reduced fracture of the high temperature extrusion die.

Having described the invention certain modifications are contemplated as falling within the scope of the invention For example, various types of jacket pressure responsive means can be used, such as a hydraulic, pneumatic or biasing systems Also, various configurations of dies can be used and various types of extrusion material. In addition, the inner and supporting portions of the die may be integrally or separately formed.

What is claimed is:

I. An extrusion system comprising;

a die including an inner portion adapted to be dynamically operated at elevated temperature and a supporting outer portion,

a pressure means adapted to force an extrusion material through said die,

pressure sensing means coupled with said pressure means for sensing the pressure applied by said pressure means, and

first pressure generating means coupled from said sensing means to said die for applying a compressive balancing force to said die on an external surface thereof in response to changes in said pressure applied by said pressure means.

2. An extrusion system as defined in claim 1 further comprising displacement sensing means associated with said die for sensing the displacement of said die and second pressure generating means responsive to said displacement sensing means for applying a force to said die at said external surface.

3. An extrusion system as defined in claim 2 wherein said displacement sensing means is located within a portion of the inner portion of said die.

4. An extrusion system as defined in claim 2 further com prising pressure control means operatively coupled between said second pressure generating means and said external surface of said die.

5. An extrusion system as defined in claim 2 and further comprising an electronic amplifying means coupled between said displacement sensing means and said second pressure generating means, for amplifying the signal from said displacement sensing means.

6. An extrusion system as defined in claim 1 wherein said pressure means included a piston and piston driving arrangement.

7. An extrusion system as defined in claim 1 further comprising means for heating the internal portion of said die 8. An extrusion system as defined in claim 1 further comprising a pressure control means operatively coupled between said pressure sensing means and said external surface of said die.

9. An extrusion system comprising:

a die including an inner portion adapted to be dynamically operated at elevated temperatures and a supporting outer portion, pressure means adapted to force an extrusion material through said die,

displacement sensing means associated with said die for sensing the radial displacement of said die, and

pressure generating means coupled from said displacement sensing means to said die for applying a radially compressive balancing force to said die on an external surface thereof in response to changes in said radial displacement of said die. 

1. An extrusion system comprising; a die including an inner portion adapted to be dynamically operated at elevated temperature and a supporting outer portion, a pressure means adapted to force an extrusion material through said die, pressure sensing means coupled with said pressure means for sensing the pressure applied by said pressure means, and first pressure generating means coupled from said sensing means to said die for applying a compressive balancing force to said die on an external surface thereof in response to changes in said pressure applied by said pressure means.
 2. An extrusion system as defined in claim 1 further comprising displacement sensing means associated with said die for sensing the displacement of said die and second pressure generating means responsive to said displacement sensing means for applying a force to said die at said external surface.
 3. An extrusion system as defined in claim 2 wherein said displacement sensing means is located within a portion of the inner portion of said die.
 4. An extrusion system as defined in claim 2 further comprising pressure control means operatively coupled between said second pressure generating means And said external surface of said die.
 5. An extrusion system as defined in claim 2 and further comprising an electronic amplifying means coupled between said displacement sensing means and said second pressure generating means, for amplifying the signal from said displacement sensing means.
 6. An extrusion system as defined in claim 1 wherein said pressure means included a piston and piston driving arrangement.
 7. An extrusion system as defined in claim 1 further comprising means for heating the internal portion of said die.
 8. An extrusion system as defined in claim 1 further comprising a pressure control means operatively coupled between said pressure sensing means and said external surface of said die.
 9. An extrusion system comprising: a die including an inner portion adapted to be dynamically operated at elevated temperatures and a supporting outer portion, pressure means adapted to force an extrusion material through said die, displacement sensing means associated with said die for sensing the radial displacement of said die, and pressure generating means coupled from said displacement sensing means to said die for applying a radially compressive balancing force to said die on an external surface thereof in response to changes in said radial displacement of said die. 